Magnetic material



av, 13, 1945. A. F. BANDUR ET AL 2,388,664

MAGNETIC MATERIAL Filed NOV. 5, 1942 INVENTORS A. A BA NOUR FD/LLl/VGFR A. /V. OGDEN 8) A?- ATTORNEY Patented Nov. 13, 1945 MAGNETIC MATERIAL Adolph F. Bandur, Berwyn, Joy F. Riverside, and Arthur N. Ogden,

Dillinger, Chicago, Ill.,

assignors to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application November 5, 1942, Serial No. 464,656

7 Claims.

This invention relates to magnetic materials and more particularly to a magnetic material having a stabilized permeability over a given temperature range.

Magnetic bodies comprising compressed, finely divided magnetic material in the form of dust or of assembled, thin laminations of magnetic material, are extensively used as cores for loading coils, filtering coils, transformers, and similar transmission apparatus in telephone circuits. A core having a permeability which varies with temperature is, of course, undesirable in many instances, since such a core will cause a coil with which it is associated to have an inductance which varies with temperature. A core of this type, when included in a high quality transmission line, adversely affects the transmission characteristics of the line.

An object of the present invention is to provide a magnetic material having a stabilized permeability over a given'temperature range.

This object is obtained in accordance with this invention by mixing with the magnetic alloy a dimensionally and structurally stable material which is substantially non-conductive electrically and inert magnetically, and utilizing the hardness and thermal expansion thereof to control the air gap between the particles of the magnetic alloy.

Other objects and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the drawing, wherein the single figure illustrates a dust core made in accordance with the present invention. While, for convenience, the invention will be described in connection with the preparation of a. permalloy, it will be understood that the process to be described is suitable for stabilizing many other magnetic materials merely by varying the proportions of stabilizer material.

A magnetic core material may be prepared as described in U. 5. Patent 2,158,132 to V. E. Legg, issued May 16, 1939, comprising 82% nickel, 16% iron, and 2% molybdenum. These materials are alloyed and ground to a powder-like fineness, and the powder mixed with a sufiicient amount of an inert refractory insulating material such as that described in U. S. Patent 2,105,070, issued to A. F. Bandur, January 11, 1938, to form an insulating coating over the particles. A filler material of talc and sodium silicate amounting to approximately 15% of the bulk of the dust core is then added. The powdered insulated particles are then compressed to the desired shape to form a magnetic core. Such a dust core will have a permeability which varies approximately .15% over a range oftemperature from 55 F. to F., the permeability increasing as the temperature increases.

This change in permeability apparently is due to expansion of the metallic particles and the consequent decrease in the size of the gaps between the particles, the tale and sodium silicate filler being relatively soft and compressible. By substituting for a part of the filler material a powdered, inert magnetically and non-conductive .electrically, material having a resistance to compression great enough so that, under the internal pressures developed in the core, this material will not be appreciably deformed, and which tends to expand as the temperature rises, the size of the gaps between the magnetic particles may be maintained substantially constant thereby tending to stabilize the permeability of the magnetic core. In practice it has been found that powdered pyrex," which has a hardness of approximately 7 on Mohs scale, gives satisfactory results. However, other materials of similar hardness and having similar expansion characteristics, for example, powdered quartz or silicon dioxide, have been found to give results similar to those obtained by using pyrex. Harder materials such as corundum or bortz may also be used. However, where the dust cores are to be compressed into the desired shapes in metallic dies, the use of extremely hard stabilizer materials such as bortz or corundum," while effective in stabilizing the permeability temperature coefilcient of the core, may tend to cause undue wear on the dies. In practice it has been found that materials having a hardness on the order of 7 on Mohs scale are sufficiently hard to stabilize without being so hard as to subject the dies to undue wear.

The exact amount of stabilizer material to be used will, of course, depend on the hardness or compression strength and the thermal coefiicient of expansion of the material. By carefully selecting the amount of stabilizer material to be used, the permeability temperature coefficient may be maintained substantially at zero over a wide range. By using an amount of stabilizer material, such as pyrex, equivalent to approximately 14% of the bulk of the dust core, and substituting this for an equivalent amount of filler material, in a magnetic material such as described, the permeability of the magnetic core may be effectively stabilized over a considerable range of temperature and no apparent change of permeability will occur in the range of temperature between 55 F. and 95 F., this range of temperature being the range ordinarily encountered in the use of the cores. Since the stabilizer material tends to expand slightly, it will be apparent that by substituting a sufilcient percentage of stabilizer material for the filler material, a slight negative permeability temperature coefficient may be obtained.

For some purposes, a desirable stabilizing effect may be obtained by combining two or more materials having the desired hardness and expansion characteristics. For example, where it is desired to reduce the permeability of a core without affecting the permeability temperature coemcient, a mixture of magnesium oxide and pyrex" may be used as a stabilizer and filler material. Since the magnesium oxide is somewhat softer than the pyrex, but substantially harder than talc, a somewhat modified stabilizing effect is obtained, thus permitting the addition of more filler material to obtain reduced permeability without obtaining a negative permeability temperature coeflicient.

While but one embodiment of this invention has been shown and described, it will be apparent that many changes and modifications may be made therein without departing from the spirit or scope of the present invention.

What is claimed is:

1. A magnetic core material having a substantially constant permeability comprising particles of an alloy containing chiefly nickel and iron, coated with an insulating material containing talc and sodium silicate compressed into a core, and a permeability stabilizing filler in said core selected from a group including powdered pyrex" glass, quartz and silicon dioxide.

2. A magnetic core comprising magnetic particles of an alloy containing chiefly nickel and iron insulated with a compressible insulating medium having added theretoa relatively incompressible filler material to stabilize the temperature effects on permeability.

3. A magnetic core comprising insulated magnetic particles of an alloy containing chiefly nickel and iron, a filler of sodium silicate and talc having mixed therewith a permeability stabilizing filler selected from the group of pulverized pyrex glass, quartz, and silicon dioxide.

4. A magnetic core comprising insulated magnetic particles of an alloy containing chiefly nickel and iron mixed with a compressible filler medium in an amount to approximately 1% of the total core body and having mixed therewith a relative incompressible filler medium to stabilize the temperature effects on permeability, the amount of said incompressible filler medium to be equal to approximately 14% of the total core body.

5. A magnetic core comprising insulated magnetic particles of an alloy containing chiefly nickel and iron having mixed therewith a mix ture of sodium silicate and talc and having mixed therewith a permeability stabilizing filler selected from the group of pulverized pyrex glass, quartz and silicon dioxide in an amount of from 1% to 14% of the total core body.

6. A magnetic core having a substantially constant permeability comprising insulatedparticies of an alloy oi. nickel, iron and molybdenum, a

talc and sodium silicate filler mixed therewith in an amount equal to 1% of the total core body, and a permeability stabilizing filler selected from the group of pulverized pyrex glass, quartz and silicon dioxide in an amount equal to 14% of the total core body.

'7. A magnetic core having a substantially constant permeability comprising insulated particles of a magnetic alloy, at filler material of talc and sodium silicate in an amount up to 14% of the total core body and mixed therewith, a permeability stabilizing filler selected from the group of pulverized pyrex glass, quartz and silicon dioxide in an amount equal to from 1%, to 14% of the total core body.

ADOLPI-I F. BANDUR. JOY F. DILLINGER. ARTHUR N. OGDEN. 

